Method for separating volatile substances from material mixtures and device for producing polyarylene sulfides

ABSTRACT

The present invention relates to a method for separating volatile substances, particularly iodine, diiodized aromatic compounds and/or mixtures thereof, from material mixtures containing said compounds. The invention further relates to a device for producing polyarylene sulphides, by means of which volatile substances, particularly iodine and diiodized aromatic compounds, can be separated from the polymers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.14/860,207 filed Sep. 21, 2015, which is a Continuation of U.S. patentapplication Ser. No. 14/397,581 filed Oct. 28, 2014, which is a nationalstage application under 35 U.S.C. §371 and claims the benefit of PCTApplication No. PCT/EP2013/058841 having an international filing date ofApr. 29, 2013, which designated the United States, which PCT applicationclaimed the benefit of European Patent Application No. 12166195.3 filedon Apr. 30, 2012, the disclosures of each of which are incorporatedherein by reference.

The present invention relates to a method for separating volatilesubstances, in particular iodine, di-iodized aromatic compounds and/ormixtures thereof from material mixtures which include these compounds.The present invention further relates to an apparatus for the productionof polyarylene sulfides with the aid of which volatile substances, inparticular iodine and di-iodized aromatic compounds can be separatedfrom the polymerizates.

In condensation polymerization processes at least one reaction productarises during the chemical reaction which has to be removed from theprocess in order to generally even enable the build-up ofmacro-molecules.

This reaction product is, however, nearly always mixed with at least onefurther substance for “reasons of equilibrium” which substance isnormally gaseous and as a monomer and/or input material can evenparticipate with the build-up of the macro-molecule and which shouldthus be fed back into the process as soon as possible.

Methods, such as e.g. polyester condensation polymerization method areknown with which, with the aid of “classical” methods such asrectification, reverse osmosis, pervaporation etc., the reactionproducts such as water or methanol and/or THF from the process aredischarged.

The chemistry and/or the process parameters for manufacturing PPS(polyphenylene sulfides) and/or PAS (polyarylene sulfides) by means ofp-DIB and elementary sulfur is, for example described in the followingpatents:

-   -   U.S. Pat. No. 4,786,713 (Copolyarylene sulfide-disulfide)    -   US 2009/0203872 (Manufacturing process for polyarylenesulfide);    -   US 2010/0105845 (Method for production of polyarylene sulfide        resin with excellent luminosity and the polyarylene sulfide        resin),    -   U.S. Pat. No. 4,746,758 (Process for preparing iodinated        aromatic compounds).

In these patents the chemistry of the manufacture of polyphenylenesulfides and/or polyarylene sulfides is described.

In the U.S. Pat. No. 4,786,713 already in the year 1988 a methodincluding statements of process parameters is described starting fromelementary sulfur and para-diiodobenzene in order to synthesize thepolymer PAS.

In the U.S. Pat. No. 4,786,713 of the year 1988 the corrosive iodine isremoved from the solidified final product by means of hot inert gasand/or vacuum, whereas in the patents of SKC the iodine is caughtthrough the addition of terminator additives towards the end of thechemical process in order to minimize the iodine content in the finalproduct. In this connection an iodine content of less than 1000 ppmshould be achieved in the final product in order to minimize and/or toprevent latter corrosion by the final product.

The substances arising in the process, such as the iodine and p-DIB(para-di-iodobenzene) are comparatively expensive, such that anefficient separation of the above components in a direct feedback,particularly of the p-DIB, into the condensation polymerization processis very important for the economic efficiency and material losses mustbe minimized. It is thus true that p-DIB should be supplied back intothe process in an as complete as possible manner and to exclude theexpensive and environmentally dangerous iodine as loss-free as possiblefor the purpose of further processing. The discharged iodine issubstantially “transformed”in a different method which is referred to as“transiodination”, to the p-DIB required for the polymer method.

Iodine containing gas mixtures from the condensation polymerizationprocess which are extracted at pressures lying beneath the triple pointof the iodine can be exclusively desublimated. For these reasons, the“typical” process units, such as rectifiers, pervaporations etc. are nolonger applicable there.

In addition to this it is particularly difficult that iodine isextremely corrosive particularly at a high purity level and necessitatesparticularly expensive materials for corresponding reactors anddifferent types of equipment.

For particularly corrosive substances, such as is the case for iodine,extremely expensive materials, such as e.g. Hastelloy and others have tobe used.

Since desublimation of iodine and p-DIB mixtures take place in vacuumshaving the order of magnitude of 1 mbar absolute pressure, therequirements and the vacuum tightness are very high and requireparticular method components and measures.

It is moreover problematic that, beneath certain pressures andtemperatures as well as supercoolings of the substances to bedesublimated, these are separated in the most different shapes andmodifications depending on the operation and kind of the apparatus.These structures can have a comparatively high or also very low densitywhich significantly influences the heat transfer and thus heat exchangersurfaces. In this connection particular modes of operation amongst otherthings of the desublimation temperatures are important for the purposeof minimization of the contact surfaces in the desublimators.

Starting here from, it is thus the object of the present invention toprovide a method which enables an as efficient as possible separation ofarising side products, for example iodine, as well as of non-reactedreactants on the manufacture of polyarylene sulfides. Likewise it is theobject of the present invention to provide an apparatus which enables anas efficient as possible separation of the previously describedsubstances from a polymer melt and/or a prepolymer melt.

This object is satisfied with regard to the method having the featuresof the patent claim 1 as well as with regard to the apparatus having thefeatures of the patent claim 9 as well as the method for producing apolyarylene sulfide having the features of claims 17. The respectivedependent patent claims in this connection represent advantageousembodiments.

In accordance with the invention thus a method for separating iodine ofat least one di-iodized aromatic compound in accordance with the generalformula III-A-I   formula II,(where A represents a bivalent aromatic radical) and/or mixturesthereof, from material mixtures comprising iodine and/or the at leastone di-iodized aromatic compound in accordance with the general formulaII, is provided, wherein

-   a) a first part of the iodine, the at least one di-iodized aromatic    compound in accordance with the general formula II, and/or the    mixture thereof is/are separated at a pressure which is equal to or    larger than the pressure which is present at the triple point of    iodine; and-   b) a second part of the iodine, the di-iodized aromatic compound in    accordance with the general formula II, and/or the mixture thereof    is/are separated at a pressure which is smaller than the pressure    which is present at the triple point of iodine;    wherein in both steps a) and b) the material mixture respectively    has temperatures at which at least iodine is present in a gaseous    state at the said pressures.

Thus, not only a condensation polymerization process per se is thesubject matter of the method underlying the invention, but rather themethod steps specifically adjoining this process which further treat,discharge and/or feedback the reaction products and the still usablereactants which escape the main process e.g. a condensationpolymerization in vapor form for reasons of equilibrium.

Thus, substances are separated which e.g. accrue during a condensationpolymerization process and/or do not react during a condensationpolymerization process during which elemental sulfur and e.g. p-DIB(para-di-iodobenzene) are built up to a macro-molecule. In thisconnection reaction products arise such as predominantly iodine, whichtogether with possibly present reactants, such as for example p-DIB,leave the individual process steps at various pressures and temperaturesin the gaseous state and are separated.

In the course of the consecutive process steps and with an advancingreaction during which the pressures sink and the temperatures increasethe substances accrue in different compositions and amounts at differentpoints of the condensation polymerization method.

That/Those process unit(s) which process(es) the separated reactionproducts which are mixed with at least one of the materials of use, haveto feed back the substances still “capable of reaction” as purely aspossible into the process and have to discharge the substances no longerrequired for the macro-molecular build-up from the method to an as largeas possible extent.

Moreover, the invention provides an apparatus which builds up themacromolecules and at the same time treats the iodine/p-DIB-gas flowswhich accrue during the condensation polymerization process which, atnormal mean and also very low pressures, i.e. at vacuums of e.g. 1 mbarand less, are discharged from the condensation polymerization steps.

Only the specific method guidance and/or the associated apparatus whichtreats these different gas flows in a new kind and manner enables largerand in particular continuous plants to be operated efficiently andcost-effectively.

In accordance with the invention it is thus provided that arising iodineas well as possibly non-reacted di-iodized aromatic compounds which areused as reactants can be separated from the arising polymer flows and/orprepolymer flows at at least two different positions of the process fora condensation polymerization method in which the di-iodized aromaticcompound is condensed by polymerization with iodine to the correspondingpolyarylene sulfides. In the event that iodine is simultaneously presentbeside non-reacted reactants (di-iodized aromatic compound) inaccordance with the present method it is likewise possible to separatemixtures of iodine and the di-iodized aromatic compound from thecorresponding polymer flows and/or prepolymer flows.

In this connection it is essential for the invention that the separationtakes place at at least two different positions of the prepolymer flowand/or polymer flow. At a first position in this connection methodconditions are present at which at least the pressure lies at or abovethat of the triple point of iodine, this means that the pressure amountsto 126 mbar (absolute pressure); at the same time sufficiently hightemperatures of the material mixture from which the said substancesshould be separated is present such that at least the iodine is presentin a gaseous aggregate state.

A further extraction of the iodine and of the di-iodized aromaticcompound and/or the mixtures thereof takes place at a further position,wherein conditions are present at which at least the pressure lies belowthe pressure present at the triple point of the iodine, this means thepressure amounts to preferably <126 mbar (absolute pressure), whereinthe material mixture from which the said substances should be separated,however, has a sufficiently high temperature so that at least the iodineis present in a gaseous state at the said pressure conditions.

However, it is likewise possible and covered by the invention that thesaid separation steps, i.e. the separation of the first part and/or ofthe second part of the previously mentioned conditions are carried out aplurality of times, this means that a plurality of separations takesplace, this means a separation is carried out at different subsequentpositions of the above-mentioned substances at the pressure conditionssuch as they are described for the first part of the separation arecarried out; furthermore, also a multiple separation of the above saidsubstances is possible at those conditions such as they are describedfor the second part of the separation.

It has surprisingly been found that a very efficient separation ofiodine, a di-iodized aromatic compound of the formula II and/or mixturesthereof from material mixtures is possible by means of the method inaccordance with the invention, so that the material mixtures can befreed nearly completely or totally (this means beneath the detectionlimit) of iodine and/or di-iodized aromatic compounds. At the same timeit has been shown that in accordance with the method in accordance withthe invention a high feedback quota with respect to iodine and/or thedi-iodized aromatic compound can be achieved.

In a preferred embodiment the material mixture from which the iodine,the di-iodized aromatic compound in accordance with the general formulaII and/or mixtures thereof should be separated, includes polyarylenesulfides which include at least one repeat unit in accordance with thegeneral formula I

A-S

   formula I,(where A represents a bivalent aromatic radical) and/or includesprepolymers thereof. Likewise a separation of prepolymers of thispolyarylene sulfide is possible. Preferably the polymers and/orprepolymers of the equation I are terminated with hydrogen.

In accordance with the invention polymers are understood as polyarylenesulfides which have more than 10 repeat units, preferably 10 to 300repeat units, particularly preferably 100 to 200 repeat units;prepolymers of polyarylene sulfides in contrast thereto representsubstances which have a repeat unit in accordance with formula I whichhave up to 10, preferably less than 5 repeat units. Preferably aprepolymer of the formula I thus has a viscosity of 0.1-10 Pas (1-100Poise) whereas the preferred viscosity of the polymers in accordancewith formula I has at least 15 to 400 Pas (150-4000 Poise), preferablyhowever 75-200 Pas (750 2000 Poise). The viscosity is determined inaccordance with MFI Melt Flow Index DIN EN ISO 1133.

The previously mentioned prepolymers and polymers which include therepeat units in accordance with formula I are generally terminated withhydrogen.

For this reason the method in accordance with the invention isparticularly suitable for the separation of iodine and/or of di-iodizedaromatic compounds of the general formula II from condensationpolymerization reactions in which polyarylene sulfide are produced bycondensation polymerization of the di-iodized aromatic compound of thegeneral formula II and sulfidation reagents, for example sulfur oralkali sulfides. This particular method guidance thus enables theproduction of highly pure polyarylene sulfides, at the same time aquasi-complete separation of the arising condensate (iodine) as well aspossibly non-reacted reactants (di-iodized aromatic compounds inaccordance with the general formula II) can be achieved.

A particularly preferred embodiment of the method in accordance with theinvention provides that the separation is carried out using acondensation polymerization reaction adapted as a two step condensationpolymerization reaction, wherein the condensation polymerization isadapted such that

-   a) in a first step the compound in accordance with the general    formula II is brought to a reaction with a sulfidation agent and a    prepolymer of the polyarylene sulfide of the general formula I is    produced by condensation polymerization; and-   b) in a second step subsequent to the first step a condensation    polymerization of the prepolymer is carried out.

In accordance with this embodiment a separation of the substances thustakes place at conditions which in the first step lie above the triplepoint of iodine and the second step beneath the triple point of iodine.

It is further preferred, when

-   a) the first separated part of the substances (this means iodine,    not reacted reactants and/or mixtures thereof) are supplied to a    distillation stage or a condensation stage and liquefy the iodine;    and-   b) the second part is supplied to a desublimation step and the    iodine is desublimated.

Due to the fact that the separation of the first part of the iodine, thedi-iodized aromatic compound and/or mixtures thereof, takes place e.g.in the first step of the condensation polymerization reaction atpressures which lie above the pressure which is present at the triplepoint of iodine, a liquification of the iodine at these said pressureconditions is possible by cooling to a temperature beneath approximately114° C. (triple point temperature of iodine). In the event that at thesame time likewise the di-iodized aromatic compounds are separated offand their melting point lies beneath the temperature at which a coolingin the distillation stage and/or condensation stage takes place thedi-iodized aromatic compound is simultaneously liquefied. In the eventthat the melting point of the di-iodized aromatic compound lies abovethe temperatures at which the previously described distillation stageand/or condensation stage are cooled a solidification of the di-iodizedaromatic compound takes place. In the distillation and/or condensationstage thus a separation of materials of iodine from the aromaticdi-iodized compound can take place under some circumstances, in theevent that the condensation stage is supplied with mixtures of theaforesaid compounds.

In accordance with this preferred embodiment a desublimation of theiodine likewise takes place which is separated as a second part from thematerial mixture. Due to the fact that the pressures here lie beneaththe pressure of the triple point of iodine (<126 mbar), no liquificationof the iodine can no longer take place at these pressure conditions,such that for a cooling below 114° C. a desublimation or solidificationof the iodine takes place. In the event that a material mixture isseparated which besides iodine also includes di-iodized aromaticcompounds in accordance with the general formula II a simultaneoussolidification of these compounds likewise takes place if their solidpoint and/or melting point lies beneath the temperature to which it iscooled in the desublimation step. In the event that its freezing pointand/or melting point lies above the temperature achieved in thedesublimation step a liquification of the di-iodized aromatic compoundwith the general formula II takes place, so that at possibly the sametime a material separation of iodine and di-iodized aromatic compoundsof the formula II can take place, in the event that the desublimationstep is supplied a mixture of iodine and compounds of the generalformula II.

In accordance with a further preferred embodiment the separation of thefirst part takes place e.g. in the condensation polymerization

-   a) at temperatures of the material mixture of 250 to 320° C.,    preferably of 260 to 320° C. and/or-   b) at pressures of 126 to 1200 mbar (absolute pressure), preferably    of 126 to 500 mbar (absolute pressure), in particular of 130 to 335    mbar (absolute pressure.

Likewise it is advantageous when the separation of the second part (e.g.in the second step of the condensation polymerization) takes place

-   a) at temperatures of the material mixture of 285 to 320° C.,    preferably of 290 to 300° C.; and/or-   b) at pressures of 0.01 to <126 mbar (absolute pressure), preferably    of 0.1 to 50 mbar (absolute pressure), in particular of 0.2 to 10    mbar (absolute pressure).

Preferred bivalent aromatic radicals A of the compound of the generalformula II and/or of the polyarylene sulfide of the formula I are inthis connection selected of the group comprising the bivalent aromaticradical A is selected from the group comprising ortho-, meta- orpara-phenyl radicals, biphenyl radicals, in particular p,p′-biphenylradicals, diphenylether radicals, in particular p,p′-diphenyletherradicals, naphthyl- and/or benzophenone radicals.

Preferred sulfidation agents by means of which the compound of thegeneral formula II can be transformed in the framework of a condensationpolymerization reaction to the polyarylene sulfides in accordance withthe formula I are in this connection selected from the group comprisingsulfur and/or alkali sulfides, wherein in particular sulfur ispreferred.

Subject matter of the present invention is also an apparatus for themanufacture of polyarylene sulfides including at least one repeat unitin accordance with the general formula I

A-S

   formula I,(where A represents a bivalent aromatic radical) produced bycondensation polymerization of a di-iodized aromatic compound inaccordance with the general formula III-A-I   formula IIusing a sulfidation agent, comprising

-   a) a precondensation stage comprising an agitating tub or a cascade    of agitating tubs composed of a plurality of agitating tubs    connected one after the other, wherein the agitating tub and/or the    first agitating tub of the cascade of agitating tubs has at least    one input possibility for the reactants, and has an outlet for the    prepolymer, and downstream of the agitating tub or the cascade of    agitating tubs further comprising;-   b) a condensation polymerization step comprising at least one    condensation polymerization reactor or a cascade of a plurality of    condensation polymerization reactors connected one after the other,    wherein the condensation polymerization reactor and/or the first    condensation polymerization reactor of the cascade of a plurality of    condensation polymerization reactors has an input possibility for    the prepolymers obtained from the first step and has a output    possibility for the condensation polymer,    wherein the precondensation stage is connected to the condensation    polymeriztion step via a product line, the agitating tub or at least    one agitating tub of the cascade of agitating tubs has at least one    drainage possibility for gaseous side products and/or not reacted    reactants, in particular iodine and/or the compound having the    general formula and the condensation polymerization reactor or at    least one condensation polymerization reactor of the cascade of    condensation polymerization reactors connected one after the other    has at least one drainage possibility for gaseous side products    and/or non-reacted reactants, in particular iodine and/or the    compound of the general formula II.

In accordance with the invention the term “drainage possibility” isunderstood as a possibility for the draining of gaseous products(exhaust vapor) from the respective agitation tubs and/or condensationpolymerization reactors.

By means of the previously mentioned apparatus a condensationpolymerization method for the production of polymers, including at leastone repeat unit in accordance with the formula I can be carried out inwhich, in the first step, a prepolymer is generated which is condensedin the second step.

The apparatus in accordance with the invention as well as the associatedcondensation polymerization method are characterized in that thecondensation polymerization reaction for the production of polyarylenesulfides is carried out in multiple steps, wherein initially aprecondensate or a prepolymer of the polyarylene sulfides is/aregenerated and subsequently the actual condensation polymerization to thefinal product takes place. The used terms prepolymer and/or polyarylenesulfide are in this connection congruent with the previously stateddefinition.

In this connection the first step is formed from an agitation tub or acascade of a plurality of agitated tubs connected one after another,wherein the reactants are provided in the first agitation tub and aprepolymer of the arylene sulfide is formed by a condensation reactionof the used starting material.

In the event that a plurality of agitation tubs are used (cascade ofagitation tubs) a transport of the prepolymer in the respectivelysubsequent agitation tub takes place, wherein successively an increaseof the polymerization degree and/or of the viscosity of the prepolymerstakes place.

Particularly preferred cascades of agitation tubs are, for example,described in the patent applications DE 103 51 085 A1 or DE 101 55 419A1 whose overall content of disclosure with respect to the cascade ofagitation tubs is made the subject matter of this application.

Moreover, the apparatus in accordance with the invention as acondensation polymerization step in a further preferred embodimentcomprises a condensation polymerization reactor and/or a cascade ofcondensation polymerization reactors connected downstream of oneanother. A corresponding condensation polymerization reactor is e.g.described in the patent application WO 2007/140926 A1 also its entirecontents of disclosure is made the subject matter of the presentinvention with respect to the condensation polymerization reactor.

A preferred embodiment of the apparatus in accordance with the inventionprovides that at least one drainage possibility of the agitation tuband/or the cascade of agitation tubs opens into a distillation columnfor the separation by distillation of the gaseous side products and/orthe non-reacted reactants, this means that at least one condensationapparatus and/or a distillation column is connected downstream of theagitation tub and/or the cascade of agitation tubs. In this distillationcolumn a purification and/or a separation of the exhaust vaporsdischarged from the agitation tub and/or the cascade of agitation tubsbecomes possible. Insofar, for example, iodine arising during thecondensation polymerization can be purified by distillation and cansubsequently be further processed, for example, can be desublimated orcrystallized. In the event that, besides iodine, also compounds of thegeneral formula II are present a separation of iodine from the compoundsin accordance with formula II can take place by means of thedistillation column.

It is further advantageous that the distillation column has a feedbackof nonreacted reactants into the agitation tub and/or into the firstagitation tub of the cascade of agitation tubs. In accordance with thispreferred embodiment it is possible to feedback the separated di-iodizedaromatic compounds in accordance with formula II, this means thereactant into the agitation tub, this means into the first step of thecondensation polymerization. This enables an extremely efficient andeconomic method guidance.

In a further advantageous embodiment the distillation column has a drainat the head side which is connected to at least one condenser ordesublimator via a supply. By means of this condenser, for example, acondensation and/or a desublimation of the iodine vapor present gaseousin the distillation column can take place.

It is further advantageous that the at least one drainage possibilityopens into at least one desublimator from the condensationpolymerization reactor and/or the cascade of the condensationpolymerization reactors connected downstream of one another. In thisconnection the possibility is included that a plurality of drainagepossibilities are present which open into a single desublimator,likewise also the possibility can be given that each drainagepossibility opens into a separate desublimator. Since in condensationpolymerization reactors conditions are generally present which liebeneath the pressure of the triple point of iodine (this means <126mbar) no condensation of the iodine vapor present in this example ingaseous state can take place from this step of the condensationpolymerization apparatus, but merely a desublimation and/or asolidification can take place. A desublimator can be used for thispurpose in accordance with the preferred embodiment of the presentinvention. The desublimator in this connection has cooled surfaces atwhich the iodine vapor can solidify. Possibly compounds in accordancewith formula II also separated in this connection, in dependence ontheir solidification point and/or the conditions present in thedesublimator, are likewise solidified and/or liquefied.

It is further preferred, when at least one distillation column isconnected downstream of the at least one desublimator which is connectedto the at least one desublimator via a line and has a head side drainand a sump side drain. By means of such a distillation column apurification of the compound in accordance with the general formula IIis further possible.

At the same time the head side drain of the previously mentioneddistillation column can open

-   a) into the condenser and/or the desublimator which is connected    downstream of the distillation column to the distillation column    which in turn is connected downstream of the agitation tub and/or    the cascade of agitation tubs, likewise it is however also possible;    that-   b) the head side drain of the distillation columns connected    downstream of the desublimator is combined with the product flow    stemming from the condenser, which is connected to the distillation    column connected downstream of the distillation column which is    connected downstream of the agitation tub and/or the cascade of    agitation tubs.

It is further preferred when the apparatus in accordance with theinvention comprises an apparatus for the generation of vacuum which is,for example, connected to the desublimator connected downstream of thecondensation polymerization reactor or to the condenser or to thedesublimator which is connected downstream of the distillation columnwhich is connected downstream of the agitation tub or the cascade ofagitation tubs of the condensation polymerization reactor. Thereby it isensured that all volatile substances stemming from the reactors, thismeans the agitation tubs and/or the cascade of agitation tubs orpolymerization reactors, is/are respectively supplied to thedistillation column and/or the desublimation units and thus aquasi-complete separation of the volatile side products and/or reactantsfrom the reaction exhaust vapors can be achieved.

The present invention will be described in the following by means of thesubsequent descriptions and by the Figures in detail, however, withoutlimiting the invention to the specific parameters illustrated there.

In this connection there is shown

FIG. 1 a first variant of the method guidance in accordance with theinvention as well as an associated apparatus for carrying out themethod; and

FIG. 2 a second variant of the method in accordance with the invention,as well as an apparatus for carrying out this method.

In the following a preparation method is described which, in a highlyeconomic and efficient kind and manner, separates gaseous substances(iodine and di-iodized aromatic compounds in accordance with formula II)either as a solid and/or as a liquid (molten solid) from specific methodsteps combines these meaningfully and feeds back a few flows into theprocess, preferably discharges iodine containing flows from the plant.

Particularly for continuous processes the iodine flows and the p-DIBflows must be removed from the process without interruption of thevacuum at vacuums of 0.1 to 300 mbar and also there above, since thefinal product must be constant with respect to its quality.

For reasons of cost and for energetic reasons the desublimation and/orrecovery process components and the plant have to be optimizedparticularly well with respect to the costs of invest and operatingcosts.

The “preparation method” is generally characterized in that

-   -   the gaseous iodine/p-DIB flows exiting at different positions        from the main flow are purified and/or discharged and preferably        iodine containing flows are separated from the process and        p-DIB-containing flows are fed back into the process for the        purpose of further reaction;    -   all iodine/p-DIB gas flows which lie above the triple point of        iodine are initially condensed and/or rectified;    -   all those iodine/p-DIB gas flows which lie beneath the triple        point of iodine are discharged from the method are initially        solidified by means of specific desublimators and are        subsequently liquefied in a further step thereafter above the        triple point;    -   it is thereby enabled to completely meaningfully combine the        different iodine/p-DIB flows and to separate these by means of        specific separation operations such as e.g. rectification below        over-pressure up to and down to vacuum and to add or to        discharge at corresponding positions of the method.

FIG. 1 shows a flow diagram of a method guidance in accordance with theinvention in which also an apparatus in accordance with the presentinvention is used. The reactants sulfur and, for example,para-di-iodobenzene are supplied from corresponding storage containersvia supply lines 11 and/or 12 to an agitation tub 10 as a first step ofthe condensation polymerization reaction. This first step is carried outat relatively high pressures, this means pressures of >126 mbar. In theagitation tub 10 and/or in a corresponding cascade of agitation tubs thereactants sulfur and p-DIB are converted to a prepolymer with relativelylow viscosity. Elemental iodine arises as a side product during thecondensation polymerization reaction. Additives, such as e.g. catalystscan be introduced at suitable positions via supply lines 14, e.g. intothe supply lines 11 or 12, the agitation tub 10 or the condensationpolymerization reactors 20 a and/or 20 b. The agitation tub 10 has adrain 101 via which the accruing iodine as well as e.g. non-reactedp-DIB can be supplied to a distillation column 102. In the distillationcolumn 102 a separation of the iodine and of the p-DIB takes place,which p-DIB can be fed back to the agitation tub 10 via a supply line15, for example, as a product discharged sump side and can thus berecycled. The iodine can be discharged at the head side via a drain 103and can be supplied to a condenser 104 where a correspondingcondensation of the iodine to molten iodine can take place.

The agitation tub 10 is in this connection operated at temperatures atwhich iodine is present in the gaseous state at the correspondingpressures of ≧126 mbar and can thus be correspondingly easily removedfrom the accruing prepolymers. The prepolymer is supplied via aconnection line 13 to a condensation polymerization reactor which in thecase of the example illustrated in FIG. 1, is of two-step design andwhich has a first condensation polymerization reactor 20 a and a secondcondensation polymerization reactor 20 b. The condensationpolymerization reactors are connected to one another via a melt line 21.Alternatively, the two reactors 20 a and 20 b can also be formed as aunit in which the corresponding steps are separated internally from oneanother. In the consecutive condensation polymerization reactors 20 aand 20 b a build-up of the degree of polymerization of the correspondingpolyarylene sulfide, for example of the polyphenyl sulfide (PPS) takesplace. In this connection iodine again arises as a gaseous side productand/or not yet reacted p-DIB can be included in the arising polymermelts. Both condensation polymerization reactors 20 a and 20 b havedrains 201 and 201′ via which the gaseous products can be supplied fromthe respective condensation polymerization reactors 20 a and/or 20 b toa desublimator 202. Likewise the possibility is given that a pluralityof desublimators are connected one after another in order to increasethe separation performance. Since pressures are present in thecondensation polymerization reactors 20 a and 20 b which lie beneath thepressure present at the triple point of iodine (<126 mbar) nosolidification of the iodine separated from the reactors 20 a and 20 bin the gaseous aggregate state is no longer possible under theseconditions; merely a solidification and/or desublimation of the iodinecan still take place. In the desublimator 202 thus a separation ofiodine as a solid substance at, for example, cooled parts of thedesublimator with which the iodine flows withdrawn from the reactors 20a and 20 b come into contact takes place. The pressures in thecondensation polymerization reactors 20 a and 20 b are in thisconnection set in such a way that lower pressure conditions are presentin the reactor 20 b than in the reactor 20 a. The final polymer melt cantake place via a output possibility 22 from the reactor 20 b. Iodineseparated in the desublimator 202 can be supplied via an outputpossibility and a supply line 205 to a further column 206 where aseparation by means of distillation of the iodine at suitable pressureconditions at which the iodine undergoes a phase transition from liquidto gaseous can take place. In this connection iodine is discharged as agaseous head side product 207 and is withdrawn and can be extracted forthe external recylcing of the column. In this connection likewise acombination of this flow 207 with the iodine flows 103, extracted fromthe distillation column 102 and condensed in the condenser 104 ispossible, wherein a line 105 is combined with the head side extractionpossibility 207 of the column 206 from the condenser. Instead of thecondenser 104 also a desublimator can be provided. The combined iodineflows 209 can thus be supplied to an external recycling. Likewise it ispossible that the iodine flow 207 extracted at the head side of thecolumn 206 is supplied to the condenser 104 in order to initiallyachieve a liquification of the iodine there. The column 206 at the sumpside has a further outlet 208 for side products or reactants, such asfor example p-DIB. The extraction of the iodine separated in thedesublimator 202 can, for example, take place thereby that thetemperature in the desublimator is time-wise increased so that again aphase transition from solid to gaseous of the iodine separated theretakes place and thus a gaseous iodine flow can be provided in the column206 via the supply line 205. Alternatively or additionally it is alsopossible to increase the pressures so that iodine separated in thedesublimator 202 can run through a phase transition from solid to liquidso that a liquid iodine flow can be supplied to the column 206 in thesupply line 205. Moreover the apparatus in accordance with the inventionin accordance with the example in FIG. 1 has an apparatus for thegeneration of a vacuum 30 which is connected to the desublimator 202and/or to the condenser 104 via corresponding vacuum lines 32 and 33.The apparatus for the generation of the vacuum 30 moreover has an outletfor exhaust gases 31.

FIG. 2 shows a further embodiment of the apparatus in accordance withthe invention in which like components as are illustrated in FIG. 1 areprovided with the same reference numerals. Also the apparatus inaccordance with FIG. 2 has an agitation tub 10 with supply lines 11 forsulfur and supply lines 12 for p-DIB, wherein, for example, in thesupply line 12 and/or the agitation tub 10 further additives and/orcatalysts can still be supplied via supply lines 12 a and/or 14. Acondensation polymerization of the reactants to a prepolymer takes placein the agitation tub 10. In analogy to FIG. 1 also the agitation tub 10in accordance with FIG. 2 has a drain 101 and is connected to adistillation column 102. The prepolymer is supplied via a supply line 13to a condensation polymerization reactor 20 designed as a multistepcondensation polymerization reactor which has drains 201 a and 201 b atdifferent positions for gaseous side products such as, for example,iodine and/or reactants, such as, for example p-DIB. These drains 201 aand 201 b respectively lead to a desublimator 202 a and/or 202 b. Thedesublimators 202 a and 202 b are connected to an apparatus 30 for thegeneration of vacuum via respectively separate vacuum lines 32 a and/or32 b. The iodine flows from the desublimators 202 a and/or 202 b arerespectively supplied to a collector 204 via a supply line 203 a and/or203 b and from there are supplied to a downstream distillation column206 via a supply line 205. The iodine flow 207 extracted at the headside is condensed and/or solidified in a condenser 104 and/or adesublimator together with that extracted from the distillation columnconnected downstream of the first step 10 and can, for example, beextracted as a so-called collected iodine flow 105 and/or as solidiodine. For the further purification likewise a feedback 106 into thecolumn 102 is possible. Moreover, the column 206 can have a furtherdrain 210 via which, for example, p-DIB purified there can initiallyagain be supplied to the condensation polymerization reactor 20.However, likewise also a discharge into the condensation polymerizationreactor 10 is possible.

The invention claimed is:
 1. A method for producing a polyarylenesulfide including at least one repeat unit of the following generalformula I, the method comprising: performing a condensation of adi-iodized aromatic compound of the following general formula II using asulfidation agent, wherein a material mixture comprising iodine and/orthe at least one di-iodized aromatic compound of the general formula IIis separated during the condensation step by a method, characterized inthat a) a first part of the material mixture is separated at a pressurewhich is equal to or larger than the pressure which is present at thetriple point of iodine; and b) a second part of the material mixture isseparated at a pressure which is smaller than the pressure which ispresent at the triple point of iodine; wherein in both steps a) and b),the material mixture respectively has temperatures at which at leastiodine is present in a gaseous state at the said pressures:

A-S

  Formula II-A-I   Formula II In the Formulae I and II, A represents a bivalentaromatic radical.
 2. The method in accordance with claim 1, wherein thecondensation step comprises: reacting the compound of the generalformula II using the sulfidation agent to produce a prepolymer of thepolyarylene sulfide of the general formula I; and condensationpolymerizing the prepolymer.
 3. The method in accordance with claim 2,wherein the separation of the material mixture is performed during eachof the steps of producing the prepolymer and polymerizing theprepolymer.
 4. The method in accordance with claim 3, wherein the stepof producing the prepolymer and the separation of the first part thereintakes place at a) the temperature of the material mixture of 250 to 320°C.; and/or b) at the pressure of ≧126 mbar (absolute pressure).
 5. Themethod in accordance with claim 3, wherein the step of polymerizing theprepolymer and the separation of the second part therein takes place ata) the temperature of the material mixture of 285 to 320° C.; and/or b)at the pressure of <126 mbar (absolute pressure).
 6. The method inaccordance with claim 2, wherein the steps of producing the prepolymerand polymerizing the prepolymer are continuously performed, and theseparation of material mixture is performed during each of the steps ofproducing the prepolymer and polymerizing the prepolymer, therebycontinuously separating and draining the first and the second parts ofthe material mixture, respectively.
 7. The method in accordance withclaim 2, wherein the first and/or the second parts of the separatedmaterial mixture are recycled to and re-used in the step of theproducing the prepolymer.
 8. The method in accordance with claim 7,wherein the di-iodized aromatic compound of the general formula II inthe first parts of the separated material mixture is recycled to andre-used in the step of the producing the prepolymer.
 9. The method inaccordance with claim 1, wherein the first part of the separatedmaterial mixture is distilled and condensed, and liquefied.
 10. Themethod in accordance with claim 1, wherein the second part of theseparated material mixture is desublimated and distilled.
 11. The methodin accordance with claim 1, wherein the condensation step including theseparation of the iodine is performed in a reactor.
 12. The method inaccordance with claim 1, wherein the di-iodized aromatic compound of thefollowing general formula II has at least one bivalent aromatic radicalA selected from the group consisting of ortho-phenylene radical,meta-phenylene radical, para-phenylene radical, biphenylene radical,diphenylether radical, naphthylene radical and benzophenone radical. 13.The method in accordance with claim 1, wherein the sulfidation agent issulfur or alkali sulfide.
 14. The method in accordance with claim 2,wherein the prepolymer and the polyarylene sulfide include the repeatunits of the general formula I, and at least one end of the repeat unitsare terminated with hydrogen.
 15. The method in accordance with claim 2,wherein the prepolymer has a viscosity of 0.1 to 10 Pas and thepolyarylene sulfide has a viscosity of 15 to 400 Pas.